fuse ratings are based on amps... so P=IV.... amps x voltage = rms power

01-27-2013

Beatin'

Re: fuse rating = wattage rms...how?

Quote:

Originally Posted by Sub Bass Woofrz

fuse ratings are based on amps... so P=IV.... amps x voltage = rms power

my kenwood 8105D has a 60A fuse.

at 2 ohms, that's 60A x 120 volts = 7,200watts :eyebrow:

doesn't make any sense. Even if half of that wattage was turned into heat, that would still be 3,600 watts. The kenwood is rated 500wrms at 2ohms with 1,000 peak.

so.......:eyebrow:

01-27-2013

Imtjnotu

Re: fuse rating = wattage rms...how?

Quote:

Originally Posted by Beatin'

my kenwood 8105D has a 60A fuse.

at 2 ohms, that's 60A x 120 volts = 7,200watts :eyebrow:

doesn't make any sense. Even if half of that wattage was turned into heat, that would still be 3,600 watts. The kenwood is rated 500wrms at 2ohms with 1,000 peak.

so.......:eyebrow:

where in the fuck are u getting 120 volts from:eyebrow:

01-27-2013

04murdalanche

Re: fuse rating = wattage rms...how?

Quote:

Originally Posted by Beatin'

my kenwood 8105D has a 60A fuse.

at 2 ohms, that's 60A x 120 volts = 7,200watts :eyebrow:

doesn't make any sense. Even if half of that wattage was turned into heat, that would still be 3,600 watts. The kenwood is rated 500wrms at 2ohms with 1,000 peak.

so.......:eyebrow:

SO much fail in this post.. Smh:crap:

First off you shouldn't be multiplying times 120 considering your car runs on 12 volt, not 120..

second of all, hate to burst your bubble but your kenwood amp doesn't do anywheres near its "rated" power.

Thir.. I give up

01-27-2013

Beatin'

Re: fuse rating = wattage rms...how?

Quote:

Originally Posted by Imtjnotu

where in the fuck are u getting 120 volts from:eyebrow:

I plugged the numbers into a wattage calulator. lol

I put 60amps into 4 ohms and it gave me 120V.

I think I did it wrong. I think you use the car battery voltage and the amperage rating for the fuse.

14.4V x 60A = 864watts

Let's say the kenwood is only 70% efficient. 864 - 30% = 604.8watts

This might mean that this amp will take about 605wrms before it catches fire???

I think???:confused:

01-27-2013

trumpet

Re: fuse rating = wattage rms...how?

This calculation is only an estimate of what the amplifier is capable of putting out. No, it does not mean that at the watts you come up with the amp will catch fire. Fuses blow slowly, and they will handle more than their rating says for brief moments. Some fuses blow more slowly than others. With music playing the amp will rarely be at maximum output unless you run it wide open all the time.

01-28-2013

zako

Re: fuse rating = wattage rms...how?

The problem is how do you know amplifier efficiency? The difference between 60% and 75% could change the estimate. I do get suspicions when a company X makes a claim about the RMS power of their product that's completely out of line with comparable amplifiers that use a similar fuse size.

01-30-2013

n2audio

Re: fuse rating = wattage rms...how?

Quote:

Originally Posted by Beatin'

I think I did it wrong. I think you use the car battery voltage and the amperage rating for the fuse.

Ya think?! :eyebrow:

Quote:

14.4V x 60A = 864watts

Let's say the kenwood is only 70% efficient. 864 - 30% = 604.8watts

This might mean that this amp will take about 605wrms before it catches fire???

I think???:confused:

Generally, yes. It's not an exact representation of power output by any stretch of the imagination.
It's a rough estimate of maximum continuous power the amp should be capable of. This approximation is usually reserved for the ultra-budget amps that you KNOW are listing inaccurate specs.

04murdalanche commented that your amp is no where near capable of rated power -- if it were the 8104 I wouldn't argue, but it APPEARS the 9105/8105's are improvements on the old amps, and I wouldn't be surprised if it actually DOES do rated power.

01-30-2013

gckless

Re: fuse rating = wattage rms...how?

Quote:

Originally Posted by trumpet

This calculation is only an estimate of what the amplifier is capable of putting out. No, it does not mean that at the watts you come up with the amp will catch fire. Fuses blow slowly, and they will handle more than their rating says for brief moments. Some fuses blow more slowly than others. With music playing the amp will rarely be at maximum output unless you run it wide open all the time.

This. Not to mention, you have no idea what the efficiency is, if the manufacturer put the correct size fuses, if it does rated, etc. There's a whole list of reasons why this method is inaccurate, but it will typically get you in a ballpark. The same ballpark you would be in if you just went off of manufacturer's ratings.

01-30-2013

Falcons

Re: fuse rating = wattage rms...how?

get an oscope/dmm/clamp meter /thread

01-30-2013

mclerico83

Re: fuse rating = wattage rms...how?

yea because i have looked at some old school us made amps that had amps that had 120 amps but max current draw was over 250 amps trying to find the manual now lol

01-30-2013

04murdalanche

Re: fuse rating = wattage rms...how?

Quote:

Originally Posted by n2audio

04murdalanche commented that your amp is no where near capable of rated power -- if it were the 8104 I wouldn't argue, but it APPEARS the 9105/8105's are improvements on the old amps, and I wouldn't be surprised if it actually DOES do rated power.